Phonograph record disk



zaad/g E. SEVERIN PHONOGRAPH RECORD DISK Filed Sept. 28, 1957 --Nov. l2, 1940.

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Patented Nov. 12, 10940 UNITED STATES Parent cerr-ce Application September 28, 1937 Serial No. 166,201

' In Germany September 28, 1936 4 Claims.

This invention refers to improved phonograph record disks with which the disturbing noises, generally called background noises, are considerably reduced. These noises are known to `be `5 caused mainly by the granular particles generally contained in the disk material. The point of the stilus or needle immerses more deeply into the softer mass between the solid granular particles and is lifted a little by passing over a grain in an electric sound box a voltage, the frequency and amplitude of which depends on the size and distribution of the grains in the disk material.

It has been proposed to avoid this drawback by using a homogeneous thermoplastic disk material, such as resins, polyvinyl-condensation products or cellulose-derivatives, instead of the usual mixtures of Igranular llers, such as slate 20 powder, ock, barite and the like, with a binder.

But the purpose has not been attained in that such disks still have a considerable background noise, especially hissing For the same purpose it has been suggested to use a iiller material of 25 extreme neness the grain size not exceeding for instance 0.001 mm.; but also this proposition does not give satisfactory results.

As mentioned above these disagreeable background noises in connection with disks of inho- 30 mogeneous materials are caused by impulses or impacts given to the stilus in very short intervals followed by corresponding movements of the anchor and by jerky voltages of the tone box or similar mechanism.

35 Figure 1 of the drawing illustrates the origin of these voltage impulses. The differently sized grains 2 imbedded within the disc material offer to the sliding stilus a mechanical resistance different frorn the resistance of the binding mate- 40 rial situated between the grains; the figure shows the voltage impulses following each other in irregular temporary intervals and having diierent magnitudes. The examination of such an impulse regarding to its frequency shows, as illus- 45 tratcd in Figure 2, a frequency-spectrum extending from up to C0 cycles with falling amplitude. If a plurality of such impulses follow each other irregularly, the amplitudes of the single frequency-spectra sum up without substantial 50 change of the frequency distribution. From this it is evident that backgrcund noises having a spectrum of 0 up to w cycles can not be avoided if an inhomogeneous disk material is used containing grains of different size or grains of same 55 size but of irregular distribution.`

receiving thus an additional impulse and causing v (Cl. 10G-f1.5)

If however the impulses follow each other regularly, the spectrum of the voltage caused by the impulses can be represented by a base-frequency and its higher waves. Consequently a necessary condition for inhomogeneous disk material offer- A ing as little backnoise as possible is a certain and constant grain-size and simultaneously a regular distribution of the grains so that the noise has a certain base-frequency.v It then is possible to so choosethe size of the grain that this base-frequency is situated at or above the frequencylimit of the `frequency to be transferred. This grain size must not exceed a certain upper value, as otherwise the base-frequency of the noise will be too low; this size must not exceed a certain lower limit, as otherwise the character of the disk approaches the character of a homogeneous disk having the disadvantages mentioned above amongst which the most troublesome is the hissing The necessary regular distribution ofl the grains can be obtained to a considerable and satisfactory degree by properly choosing the ratio of granular ller and binder so that the grains after the pressing of the disk are situated closely adjacent to and in touch with each other, without substantial intervals, as illustrated in the Figure 3.

Figure 4 illustrates the distribution ofthe impact-voltages cf such a material. Theimpacts follow each other in regular intervals T1. The analysis of the base-wave shows that its maxima and minima have the same time-interval T1.

v It'will be diiiicult if not impossible to prepare a granular material of suiciently small and equal and constant grains by the grinding and sifting of any original natural material such as spar, barite, slate or the like. Especially crystalline materials will break during grinding into needlelike particles passing a sieve in their longitudinal direction although the length of such parti- 40 cles is far beyond the allowable limit. In any case it is necessary to subject such ground material after sieving to a further separation by air blowing or elutriating. It is, however, preferable 4 according to the present invention to use a filler material obtained chemically or synthetically by precipitation, such as precipitated calciumcarbonate or barium-sulphate or precipitated silica. It is of advantage if the precipitated particles are substantially amorphous. Suitablel materials of suitable grain-size are also obtained by precipitating colloidal solutions by addition of electrolytes. k

The grain size suitable for the purpose of the invention and which shall be neither too large nor too small as mentioned before, has been found to be between 0.030 and 0.001 mm.

Also the preferred material obtained by precipitation should be subjected to a further shifting operation after grinding and sieving in order to ensure a material of substantially equal grainsize.

The following calculation allows to nd out the suitable grain-size:

The disk Velocity in the last groove of the disk is about 30 mm. per second if the turntable makes 78 revolutions per minute. If the base frequency caused by the grain-size shall be about 15,000 cycles, the grain size must be Tacco If the turntable makes only 331/3 revolutions per minute the grain-size must be 0.008 mm. The frequencies may be assumed to be arranged around a preferred maximum, following the law of distribution of Gauss; asvshown in Figure 5 for a grain size corresponding to a frequency of 15,000 cycles and for a smaller size corresponding to a frequency of 20,000 cycles, it is advisable to choose the grain size so small that the part of the spectrum reaching into the frequency of the human ear has but little amplitudes this being the fact for the curve with the greatest amplitude at 20,000 cycles corresponding to a grain size of 0.015 mm. respectively 0.006 mm.

It is evidently not necessary to keep these grain sizes exactly and absolutely, but any greater deviations are to be avoided, say more than 50% from the middle Value to both sides, if the middle value is 0.02 mm.; if the grain size is smaller, say 0.005 mm. still greater deviations may be allowed.

As stated before not only the substantial equality of the grain size is essential but also the uniform distribution of the grains. This condition can be attained to a practically satisfactory extent by so choosing the ratio of granular ller and binder that the single grains are pressed close together during the making of the disk. This correct ratio can be easily determined from the specific weights of the used materials. It further is obvious that a very good and intimate mixing, generally for several hours, is necessary for obtaining the maximum of homogeneous distribution.

No special binders are essential for the purpose of the present invention and all binders used in the art may be used, such as natural and artificial resins, alone or in mixture, gelatine or similar proteins, lacquer compositions and the like.

What I claim is:

1. A phonograph record disk consisting of a mixture of a granular filler and a binder, the grains of the filler being all of substantially uniform grain size and the ratio of filler and binder being so that the grains are situated close together without substantial intervals.

2. A phonograph record disk in accordance With claim 1 and in which the size of the grains being substantially equal is between 0.001 and 0.020 mm.

3. A phonograph record disk in accordance With claim l and in which the deviation of the size of the grains does not exceed 50% of the middle value to both sides.

4. A composition of matter for making phonograph record disks consisting of a mixture of a granular filler and a binder the grains of the liller being of substantially equal grain size and not varying more than 50% from a middle value which is between 0.001 and 0.020 mm., and the ratio of ller and binder being so that after the pressing of the composition into the shape of the disks, the grains are situated close together without substantial intervals.

EDWIN SEVERIN. 

